Property never stops needing something, and property maintenance never takes a break. Even in the dead of winter, there is something that needs to be done. Where lakes and ponds are the properties in question, this is may be more of a truth than some other areas of your property.
Spring lake maintenance
Fertilization of ponds and lakes should start as early as possible in the spring. This will not only jump start your fish, but it will also add that nice green tint that phytoplankton pond algae gives the water. This will shade the bottom, and keep weeds and pond scum from having a chance to get an early start. This program of fertilization should be carried out every couple of weeks until the end of summer, or until a secchi disk disappears at less than 18 inches.
Spring is also the perfect time to get a handle on those aquatic weeds and string algae problems that may have beaten you to the punch. You should stay on top of this until the problem is gone. If you do this right, and follow up promptly and correctly, you might just avoid the annual weed takeover. Pay attention to the label directions, especially with regard to temperatures so you don't end up wasting costly chemicals if the weather is too cold.
This should also give you the opportunity to do the most important part of lake ownership: Enjoy it!
Summer lake maintenance
If you need a fertilization program, you should continue it throughout the summer. If you have lake weed problems at this stage, handle them as soon as possible, and use good follow up, and again, enjoy the lake.
Fall lake maintenance
Test your pond pH. If the pH needs to be raised, now is a good time to find out, and start making plans to add lime late in the fall, or during the winter. By this time, your lake weed problems should either be solved for the year, or the weeds should be too mature to properly treat. Manual or mechanical removal is about the only way to deal with them at this stage. This is also a good time to think about things like dredging, draw down, or raising the water level. It is also the best time to start putting together plans for improvements to docks, slips, boathouses, pump houses and other lake and pond buildings.
Winter lake maintenance
If you did your planning in the fall, you should now have all the materials and plans laid out for late fall, and early winter lake projects, so just jump in and get started.
If you plan to draw the lake down for dock repairs, dredging, or weed removal, don't lime beforehand. It will be possible to do a more effective job during the draw down stage. Just do all your maintenance and building work, dredging, or whatever else you planned on doing, and lime when your done and before you start raising the water level.
If you don't plan a draw down, lime the pond if it needs it, and if you haven't already done so.